Fluid treatment



Aug. 31, 1965 WILLIAM KWO-WEI CHEN ET AL 3,203,887

FLUID TREATMENT Filed July 20, 1960 3 Sheets-Sheet 1 INVENTOR. WILLIAMKWO-WEI CHEN MILTON SHELDON MINTZ ATTORN EY Aug. 31, 1965 WILLIAMKWO-WEI CHEN ET AL 3,203,887

FLUID TREATMENT 3 Sheets-Sheet 5 Filed July 20, 1960 M M B m 4 5 A 9 N 4m wwwm w w w m /y f l/.l w: I m M H W \6 in i T. T 9 a w v m 7 M 4 m e.H 5 (6 5 w Wm ,6 7 1 1 Q Q H. L2 Z/ MILTON SHELDON MINTZ 4/444 4)ATTORNEY United States Patent 3,203,887 FLUID TREATMENT William Karo-WeiChen and Milton Sheldon Mintz, Stamford, Conn, assignors to The AmericanMachine and Foundry Company, a corporation of New .lersey Filed July 20,196i Ser. No. 44,117 1 Claim. (Cl. 204180) This invention relates ingeneral to multiple chamber fluid treatment devices, and, moreparticularly, to the acidification of electrodialysis stacks.

In the treatment of natural brines and other solutions byelectrodialysis, the base produced at the cathode and at polarizedinterfaces between the surface of a membrane and the solution causestroublesome precipitation if some means is not provided to counteractit. Methods have been proposed which utilize the acid produced at theanode to counteract the formation of a base elsewhere in the stack.Since the quantity of acid produced electrodialitically at the anode cannever exceed the quantity of the base produced within the stack, theseprocedures provide no safety factor and slight changes in the brine orsolution characteristics of the fluid being treated may readily upsetthe delicate electrochemical balance. For this reason, it has been amore common practice to add acid from an external source to theelectrodialysis stack. The major objection to this latter procedure isthe relatively high cost of the equipment required for introducing acidat the proper rate and pressure.

It is, therefore, an object of this invention to provide a less costlymethod for the introduction of acid into an electrodialysis stack.

It is an object of this invention to provide a process of dis ensinganions into the concentrating stream of an electrodialysis stack inwhich the process comprises the steps of maintaining in a cathodecompartment a solid material, comprising acid anions (which areliberated therefrom when in contact with water) selected from solidacids and acid salts, in substantial equilibrium with a saturatedaqueous solution of said solid material and diffusing said anions underelectrical potential through an anion selective permeable membrane intoan adjacent concentrating stream in an electrodialysis stack, wherebysaid solid material is depleted in the operation of said stack.

Another object of this invention is to provide an electrodialysis stackwhich can be operated for longer periods of time without requiringservice due to precipitation within the stack.

A further object of this invention is to provide a less costlyelectrodialysis stack which can operate for longer periods unattended.

Many other objects, advantages and features of invention reside in theparticular construction, combination and arrangement of parts involvedin the embodiment of the invention and its practice as will beunderstood from the following description and accompanying drawingwherein:

FIG. 1 is a perspective view of an electrodialysis stack;

FIG. 2 is a vertical longitudinal section through the electrodialysisstack;

FIG. 3 is a perspective view of a fragment of one end of a gasket and anadjacent membrane; and

FIG. 4 is an exploded perspective view of the elements forming theelectrodialysis stack.

Referring to the drawing in detail, FIGS. 1 and 2 show an assembledelectrodialysis stack, generally designated by the numeral 29. The stack29 is clamped between two end plates 30 and 31, which may be steel orother rigid material, by tightening the bolts 32 and drawing the endplates together. Heavier blocks of electrical insulating material 33 and34 may be disposed inside the end plates 3,Zh3,83? Patented Aug. 31,1965 3t? and 31 so that the bolts 32 are disposed beyond the center ofthe stack 29 and electrically insulated from it. The end plate 3%) andblock 33 have the electrode chamber vent pipe 35 fixed into them. Theend plate 3th also receives the intake pipes 39 and 4-1). in a likemanner, the end plate 31 receives the product and concentrate pipes 41and 42 and the electrode chamber vent pipe 37. Referring now to FIG. 4,these pipes 35, 37, 39, 40, 41 and 42 lead to fluid flow apertures 64,74, 61, 62, 70 and 71, respectively, which are formed in the elementscomprising the stack 29. These fluid flow apertures in the stackelements form manifold passages within the stack 29.

Referring now to FIG. 3, a gasket is an elongated rectangle in itsexternal shape with a central rectangular cutout portion 52. Pairs offluid flow apertures 45 and 46 at each end of the gasket 54 formmanifold passages. Communicating from one of these fluid flow apertures4-5 or 46 to the cutout chamber 52 are the small passages 47. Thus eachend of the gasket 5t? contains small passages 47 communicating withoppositely disposed fluid flow apertures to form hydraulic connections.A membrane 43 lies next to each side of each gasket 56. The membrane 48contains manifold apertures corresponding to those formed in the gaskets50. Within the central cutout portion in each gasket it) there may beplaced a screen spacer element 57.

FIGS. 2 and 4 show the arranged elements of an electrodialysis stackembodying this invention. A steel plate 30 or other reinforcementmember, a plastic block 33, and an insulating sheet contain the twofluid intake aperture 61 and 62 and also the electrode chamber ventaperture 64. Below the insulating sheet 65 lies the gasket 66 which isconsiderably thicker than the cell forming gaskets 5% so that itscentral opening 63 will provide a large electrode chamber. There are nointernal passages formed within the gasket 66 communicating with themanifold apertures 61 and 62 which it has formed in one end. Theelectrode chamber 63 contains the electrode 67 which may be of platinumfoil or other suitable material. An electrical connection 68 extendsfrom this electrode to be connected to a suitable current source. Theconnection 68 may also be seen in FIG. 1.

After the gasket 66, there is placed a sheet 69 of a porous non-wovenmaterial which is suificiently porous to allow either anions or cationsto pass while it resists the attack of chlorine or other degradationagents generated at an electrode. This sheet 69 may be made of anyporous, relatively inert material.

Following the sheet 69 there are placed a number of layers, eachconsisting of an .anion permeable membrane 48A, a gasket StlA, a cationpermeable membrane 48K, and another gasket 50B. It is to be noted thatthe gaskets 59A and 5913 are identical except that the gasket 50B is thesame as gasket 56A in the inverted position. Thus fluid may flow fromthe intake manifolds formed by the ali ned fiuid flow apertures 61 and62 into alternate chambers 52C or 52D. in a like manner, fluid flowsfrom these alternate chambers designated 52C or 52D into either amanifold formed by the fluid flow apertures 70 or a manifold formed bythe fluid flow apertures 71.

As long a series of cells may be built up in this manner as desired bystacking up the alternate layers of gaskets 50A and ShB with theinterspersed membranes 48A and 48K. At the other end of the stack, thelower end as shown in FIG. 4, there follows in reverse order anotherporous sheet 69 and another gasket 66 which contains a second electrode72. Another insulating sheet 65, another plastic block 34- and anotherplate 31 follow, each containing the fluid flow apertures 7t} and 71 andalso the electrode chamber vent aperture 74.

Referring now to FIGS. 1, 2 and 4, this invention operates in thefollowing manner. Fluid to be treated flows into the stack through pipes39 and 40 to pass through the fluid flow apertures 61 and 62. That fluidwhich passes through the fluid flow apertures 61 passes through thecentral cutout portions 52C of the alternate gaskets 50A. The fluidwhich passes through the fluid flow apertures 62 would, in a likemanner, pass through the central cutout portions 52D of the alternategaskets 5013. If the membranes 48A were anion permeable membranes andthe membranes 48K were cation permeable membranes, and if the electrodes67 and 72 were connected to a direct current source so that theelectrode 67 was a cathode and the electrode 72 was an anode,concentrating cells would be formed within the cutout portions 52C anddiluting cells would be formed within the cutout portions 5213. Thus adilute or product stream would flow from the stack through the fluidflow apertures 70 while a concentrate stream flowed from the stackthrough the fluid flow apertures 71.

Referring now to FIG. 2, an anion permeable membrane 48A is placedadjacent to each electrode compartment. The enlarged electrodecompartments 63 are each packed with a cake 25 of a solid acid salt, forexample, in a stagnant acid filled volume. One such acid salt which maybe used is sodium bisulfate. Organic acids may also be used such asoxalic or citric. Meta phosphoric acid also works. The acid salt orsolid acid may be packed into cakes as shown, it may be packed looselyinto the electrode cells, or liquid solutions of an acid may be used.The invention includes use of a reserve acid supply, preferably packedinto the electrode chamber.

As shown in FIG. 2, the electrode compartments or cells 63 are vented tothe atmosphere by the pipes 35 and 37. The upward extensions 20 and 21of these pipes 35 and 37 terminate in the closures 22. The closures 22each have a cover 23 held over them by a hinge 24. Thus the covers 23may be swung aside to introduce fluid into the electrode chambersthrough a suitable filtering material 26 which is placed within theclosures 22. The lids 23 contain the small vent apertures 27 which allowgases generated at the electrodes to escape into the atmosphere.

When the electrode 67 functions as a cathode, fluid within this cathodechamber is a saturated solution of the acid salt with which the cathodecompartment is packed. Therefore, any base produced at the cathode isimmediately counteracted by the solution. Since an anion permeablemembrane 48A is adjacent to each electrode compartment, there is noelectroendosmotic water transfer into the cathode compartment. Watertransfer by electroendosmosis is directed out of the cathodecompartment, but an equilibrium is maintained by normal osmosis whichresults in water transfer into the cell by virtue of its high acidconcentration.

If, as shown in FIG. 2, the electrode compartment on the right was notpacked with an acid salt and was formed conventionally, thiselectrodialysis stack could operate over a very long period of timebefore the available acid salt packed in the cathode compartment wasused up counteracting the base produced at the cathode. Thisconstruction allows an inexpensive electrodialysis stack to be assembledto operate over a long period of time without the need for expensiveacid feeding apparatus.

As shown in FIG. 2, if both electrode compartments are packed with asuitable acid salt, there may be periodic electrical reversal of thestack (preferably every half hour).

In such a case, the current source would be reversed so that theelectrode 72 functioned as a cathode and the electrode 67 functioned asan anode. In this case the gaskets A would contain diluting cells, whilethe gaskets 50B contained concentrating cells, and the dilute streamwould flow from the stack through the fluid flow apertures 71 while theconcentrate stream flowed through the fluid flow apertures 70. In thiscase the electrode compartment containing the anode would receive waterby electroendosmosis but there need be no fluid or acid loss if astandpipe 20 or 21 is provided having a suitable volume to accommodatethe water carried into the anode compartment by electroendosmosis for agiven period of time before electrical reversal. Upon electricalreversal, the electrode compartment which was functioning as an anodewould now function as a cathode and excess water would be transferredback into the body of the stack with no loss of the acid salt insolution through the anion permeable membrane.

If it is desired to add acid to the concentrate stream, the stack may beconstructed so that a concentrate cell is adjacent to the cathode. Byusing either a very strong acid or a more porous anion membrane adjacentto the cathode compartment, the acid may be permitted to diffuse intothe adjacent concentrating cell.

While a given construction of an electrodialysis stack is shown havingparallel flow through it, this invention is not limited to anyparticular stack construction. It may be used in any electrodialysisstack utilizing series flow, parallel flow or any combination thereof.This invention may be used in stacks which are built up as shown in thisapplication, or it may be used in connection with circular or otherstack construction.

What is claimed is:

The process of dispensing anions into the concentrating stream of anelectrodialysis stack comprising the steps of:

(a) maintaining in a cathode compartment a solid material, comprisingacid anions selected from solid acids and acid salts, in substantialequilibrium with a saturated aqueous solution of said solid material and(b) diffusing said anions under electrical potential through an anionselective permeable membrane into an adjacent concentrating stream in anelectrodialysis stack, whereby said solid material is depleted in theoperation of said stack.

References Cited by the Examiner UNITED STATES PATENTS 2,810,686 10/57Bodamer 204301 2,855,280 10/58 McConnaughey 23-232 2,937,126 5/60Rosenberg 204301 2,995,425 8/61 Fuhrmann 23-253 3,003,940 10/61 Mason204-480 3,017,338 1/62 Butler 204 18O OTHER REFERENCES Kirkham: IonExchange Membranes for Water Conditioning, reprinted from Combustion,June 1956, 7 pages.

WINSTON A. DOUGLAS, Primary Examiner.

JOHN H. MACK, Examiner.

